Since the advent of pressure-sensitive adhesives, such materials have been used in a variety of applications requiring the attachment of a relatively thin, flexible layer of material to an underlying surface. Pressure-sensitive adhesives, for example, have been extensively used to attach labels, stickers, decorative strips, tapes and the like, and are even being considered for use with postage stamps, all of the preceding and similar articles being sometimes referred to herein as "labels."
In the industrial area, pressure-sensitive adhesives find application, for example, in the attachment of decorative automotive striping, the attachment of decorative designs, informational text, and in many other areas too numerous to mention. Typically, such applications involve covering one surface of the material to be attached with the layer of pressure-sensitive adhesive, and then covering the exposed adhesive with a removeable release-material, usually paper, which is discarded prior to attachment of the material, or substrate, to the surface on which it is required.
In the past, the laminations described have commonly been prepared by dissolving the pressure-sensitive adhesive in a suitable solvent, and then coating the adhesive solution on the substrate whose subsequent attachment to a particular surface is required. The process of coating the adhesive solution on the substrate may be successfully accomplished by means of any of the standard coating techniques such as transfer coating, roll coating, or some such equilvalent method. However, while resort may be had to such techniques, they frequently have significant disadvantages with respect to the application of pressure-sensitive adhesives, particularly with respect to the substrates comtemplated by the invention. For instance, the use of solvents is often undesirable for the variety of reasons, including the fact that it frequently entails extensive and costly measures to assure compliance with environmental rules and regulations, including the recovery of the solvents employed. Not only do solvent recovery systems require very substantial investments in terms of Equipment, but the operation of the solvent recovery process is expensive in terms of energy consumption, as well as in the manpower required to operate the equipment. In addition, solvent recovery systems enevitably involve the loss of at least some of the solvent being recovered, creating additional expense.
Furthermore, particularly in the case of industrial applications, substantial thicknesses of adhesive coatings are required, making solvent depositions difficult, and sometimes impractical. A further disadvantage stems from the fact that coatings systems oftentimes result in coatings of varying thickness, making it difficult to carry out printing of the coated laminates which may be required subsequent to the coating operation. Still another disadvantage of coating processes is that they are relatively slow, limiting the amount of production that can be achieved through their use